1865.] Geology and Palaeontology . 475 



Nordoestlichen Gebirge von Graubiinden,' by Professor G. Theobald. 

 The author has good grounds for dilating, in his opening chapter, on 

 the difficulty of geological surveying in this mountainous region, 

 which is one of the most intricate and disturbed in Switzerland, and 

 where the rocks are often masked by glaciers and fields of snow, while 

 extraordinary contortions and even overturnings of the strata are so 

 abundant as to become commonplace occurrences. Add to these 

 difficulties that the rocks are often highly metamorphosed, so 

 that different beds frequently look alike, while the same rock appears 

 under a dozen different aspects, and that the fossils have generally 

 been obliterated by the metamorphism, and we may then picture to 

 ourselves the amount of patient and conscientious labour required of 

 Professor Theobald during his survey of this district. 



But this book, besides containing a complete geological description 

 of the district to which it relates, includes a short essay on the physi- 

 cal features of the Alps, in which the author adopts the theory just 

 explained, and describes in detail the central masses which he has 

 examined. He observes that they consist of crystalline rocks, chiefly 

 Gneiss, but sometimes Hornblende-schist and Mica-schist, while true 

 granite is much less abundant than has hitherto been supposed. 

 Around and between the central masses are zones of sedimentary 

 strata, often metamorphosed into clay-slate, &c, the crystalline rocks 

 having been thrust up from beneath them in anticlinal ridges, or more 

 frequently in excessively contorted or reversed folds, not suddenly, 

 nor by any grand convulsion, but slowly and silently. Professor 

 Theobald truly remarks that the Alps cannot be understood geo- 

 graphically if their stratigraphical features be not taken into con- 

 sideration. 



Having thus indicated the chief features of this theory of the Alps, 

 we must leave it to those particularly interested in the subject to read 

 for themselves the descriptions of the different types of central-masses, 

 and the numerous cases in which surface-form is shown to be de- 

 pendent upon geological structure. 



The last volume of the ' Bulletin de la Societe Geologique de 

 France,' contains an important paper by M. Levallois, entitled ' Les 

 couches de jonction du Trias et du Lias dans la Lorraine et dans la 

 Souabe,' &c. It may be considered the continuation of his paper on 

 the ' Gres d'Hettange,' published in the previous volume. The author 

 brings to the subject a larger share of philosophical coolness than 

 French geologists usually possess, for he declares his belief that the 

 boundary line of the Trias and Lias is destined to be the subject of 

 eternal dispute. 



The passage-beds, however, are shown by him to occur uninter- 

 ruptedly and with a uniform constitution from the Ardennes to 

 Morvan ; they are composed chiefly of a sandstone which is the ' gres 

 infra-liasique ' of various authors, and which contains the fossils of the 

 zone of Avicula-contorta. In the departments of the Meurthe and 

 the Moselle and in Luxembourg they are constantly separated from 

 the Hettange beds by an unfossiliferous band of red clay more than 

 fifteen feet in thickness. He considers that the ' gres d'Hettange ' is 



